Stylus pressure adjustment means



NOV: 22, 1949 w THOMPSON 2,489,062

STYLUS PRESSURE ADJUSTMENT MEANS Filed July 28, 1947 Diql. Y 9

M f A W. F Thom 960w,

Patented Nov. 22, 1949 UNITED STA'lEii i A'lTilidT OFFICE STYLUS PRESSURE ADJUSTMENT MEANS William F. Thompson, Salina, Kans.

Application July 28, 1947, Serial No. 764,209

3 Claims.

My invention relates to an improvement in cut ting or embossing of sound track upon record ing blanks and of play-back or pick-up devices for the reproduction of such recording.

The principal objects of the invention are:

1. To provide an electro-rnagnetic control and variation of the pressure exerted upon and applied by the cutting or the reproducing stylus upon the surface of the record blank (disc or cy inder) being cut or embossed or being repro duced; in the latter case of reproduction, the contro-l and variation of pressure are upon the be tom of the sound track theretofore cut or embossed.

2. To provide an electro-magnetic damping or stabilizing of the play-back or pick-up head within which is movably inserted the reproducing stylus tracking along the sound grooves of the record.

Other objects will in part be obvious and in part be pointed out hereinafter.

To the attainment of the aforesaid objects and ends invention resides in the novel construction, combination and arrangement of parts which will first be described in detail and then be specifically pointed out in the appended claims, reference being had to the accompanying drawing in which:

Fig. 1 is an elevation, somewhat schematic, i1- lustrating the application of my invention as ap plied to disc type records.

Fig. 2 is a similar view of the invention as ap plied to a cylindrical record.

Fig. 3 is a detail View similar to Fig. l of a modification, parts being broken away.

In Fig. 1 of the drawing, 1 represents the turntable of a recording or reproducing machine, which table is constructed of magnetic material and on which the record or record blank 2 is held.

3 indicates the recording or play-back arm which lies horizontally and turns on a pivot 4 and to which arm the recording or play-back head 5 is hinged as at 6. The arm 3 and head 5 may be of any approved construction save that into the head is placed anelectro-magnet i, which is designed to draw the stylus 8 toward the record blank or record under pressure variable at the will of the operator.

An electric circuit 2 is provided which is connected to suitable source of energy IE], and in which is included a variable resistance 1!.

In the form illustrated in Fig. 2 those parts which are like corresponding parts in Fig. 1 bear the same reference number plus the index letter a and need not be re-described here. In applying my invention the core I2 of the electro-magnet '6' has its face curved to the curvature of the record or recording blank cylinder 2 while in the embodiment shown in Fig. 1 the face of the core i2 is parallel to the turn-table and disc 2.

In the cutting or embossing of electronic sound tracks upon the surface of a blank record (disc or cylinder) the depth of the cut or embossed sound groove is a factor in the making of good recording; likewise in reproduction of recorded matter th weight and stability of the play-back or pickup device is a factor in good reproduction. Material used in records; methods of manufacture, etc. vary surfaces and texture of record blanks. and repeated wear and damage of recorded sound grooves result in varying conditions of records being reproduced. To insure proper relation between the cutting or embossing stylus and the material being cut or embossed requires a convenient and precise adjustment of the pressure exerted by the stylus upon the record surface; likewise such adjustment is necessary to insure proper reproduction by the play-back or pick-up head.

The trend in modern recording and repoduction machines is toward smaller and shallower sound grooves and lighter weight pick-up heads. This results in lack of stability of pick-up heads and less surety of proper tracking of play-back stylus in sound groove. My invention in its relation to the light weight pick-up head and shallow groove increases the stability and tracking by application upon the head of a magnetic r damping due to the attraction between the 'ick-up head the moving surface of the turntable or cylinder upon which the record is held; such turntable or cylinder to be constructed of suitable magnetic material.

While record discs and cylinders are now made of non-magnetic material, should record discs and cylinders be made to include in their structure magnetic material then the attraction between the electro-magnet and the record disc or cylinder itself will effect the desired pressures between stylus and record disc or cylinder as the case may be. If both the record disc and turntable (or record cylinder and rotating spindle) are made of non-magnetic material then my invention contemplates placing a thin metal disc 53 under the record disc 2* on the turntable I (or thin metal sleeve between the record cylinder and spindle) as within the scope of my invention (see Fig. 3).

From the foregoing it will be seen that the essence of my invention lies in the provision of an electric circuit for the electro-magnet wherein means are provided by which the electromotive force may be varied to vary the magnetic efiect whereby the pressure of the recording or reproducing head may be increased or decreased in minute degree from minimum to maximum requirements necessary to produce the best recording pressure upon the record by the stylus or the best reproducing head pressure upon the record. As heretofore intimated, there is a critical point in pressure in both recording and reproducing heads at which point maximum efficiency is attained in recording and reproduction, and my invention consists of means whereby such critical pressure upon the record may be applied; adjustment by the operator of the variable resistance in the electro-magnetic circuit causing increased or decreased magnetic pull between the recording or reproducing head and the turntable upon which the record is held.

From the foregoing description taken in connection with the accompanying drawing it is thought the construction, operation and advantages of my invention will be clear to those skilled in the art.

What I claim is:

1. In art of sound recording and reproducing wherein is provided a rotatable body of magnetic material, on which the record body to be cut or played is placed and in which is provided an arm, and a stylus head with a stylus, the improvement which comprises: means for effecting a magnetic attraction between said stylus-carrying head and said rotatable body, and means for varying said attraction at will.

2. In art of sound recording and reproducing wherein is provided a rotatable body of magnetic material, on which the record body to be cut or played is placed and in which is provided an arm, and a stylus head with a stylus, the improvement which comprises: an electro-magnet in the stylus-carrying head and havin a fixed core, and an electric circuit including said electro-magnet and a variable resistance.

3. In art of sound recording and reproducing wherein is provided a rotatable body of magnetic material, on which the record body to be cut or played is placed and in which is provided an arm, and a stylus head with a stylus, the improvement which comprises: eleotro-magnetic means cooperating with said rotatable body for pressing the stylus onto the record body, and means to vary at will the degree of pressure applied.

WILLIAM F. THOMPSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,344,186 Morrison June 22, 1920 1,383,737 McQuarrie July 5, 1921 1,568,612 Morrison 1 Jan. 5, 1926 2,293,220 Rieber Aug. 18, 1942 FOREIGN PATENTS Number Country Date 98,322 Sweden Jan. 11, 1940 

